1. Field of the Invention
This invention relates to a process for producing an aromatic polyester from an aromatic diester and an aromatic dicarboxylic acid.
2. Description of the Prior Art
Aromatic polyesters derived from aromatic dicarboxylic acids and dihydric phenols have excellent chemical and physical properties such as high thermal resistance, high strength, low hygroscopicity, and high chemical and solvent resistances. Accordingly, it is known that the aromatic polyesters can be employed in a wide range of uses such as fibers, films, molded articles and coating materials.
One known method of producing these aromatic polyesters involves an interfacial polymerization comprising reacting an aqueous alkaline solution of a dihydric phenol with an aromatic dicarboxylic acid chloride dissolved in a water-immiscible organic solvent [see, for example, W. M. Eareckson, J.P.S., 40, 399, (1959)]. Another method comprises polymerizing an aromatic dicarboxylic acid and a bis-carboxylic acid ester of a dihydric phenol (see, U.S. Pat. Nos. 3,948,856 and 3,824,213). These methods, however, have some drawbacks. For example, according to U.S. Pat. No. 3,948,856 the resulting polymers are remarkably discolored, probably due to the presence of an inorganic strong acid radical, and the inorganic strong acid radical remaining in the polymers exerts an adverse effect on the properties of the polymers. Furthermore, the amount of the catalyst required is great and accordingly, the method becomes costly. Also, when the catalysts described in U.S. Pat. No. 3,824,213 are used, an undesirably long time is needed to obtain a polymer having a high degree of polymerization.
It is accordingly an object of the invention to find catalysts producing polymers free of these deficiencies.